1. Field of the Invention
The present invention relates to a thin-film electroluminescent element (hereinafter referred to as "thin-film EL element") wherein the luminescent composite is a laminated layer comprising at least a first layer and a second composite. Especially the invention relates to materials for the luminescent layer.
2. Discussion of the Relate Art
Thin-film EL elements are useful as displays because they are thin and the displaying state is very precise.
FIG. 3 is an enlarged cross-sectional view of a conventional thin-film EL element. As shown in the figure, on a transparent substrate 1, such as a glass plate, there is formed a transparent electrode 2, such as indium-tin oxide film (hereinafter referred to as "ITO film") and SiO.sub.2 film, and further on the electrode there is formed, such as by sputtering, a first insulation film 3 comprising an oxide, such as Ta.sub.2 O.sub.3 and SiO.sub.2, a nitride, such as Si.sub.3 N.sub.4, or a laminated film of the above-mentioned oxide film and nitride film.
On this first insulation film 3 a luminescent layer 4 comprising a superlattice layer is provided, and further a second insulation film 5, having the same material as the first insulation film 3, is formed. On the second insulation film 5 a back plate 6 comprising aluminum, etc. is provided. The transparent electrode 2 and the back plate 6 are connected to a power source 7 to exert the luminescence of the element.
Heretofore, regarding this thin-film EL element, only a mixture of ZnS and Mn, a material for yellow-orange color, has been put to practical use.
For a full range of color, a mixture of ZnS and Sm and a mixture of CaS and Eu have been studied as materials for red. However, a material satisfying both brightness and color purity has not been obtained.